﻿using System;
using System.Collections;
using System.Globalization;
using System.Text;
using System.Collections.Generic;


/// <summary>
/// This class encodes and decodes JSON strings.
/// Spec. details, see http://www.json.org/
/// 
/// JSON uses Arrays and Objects. These correspond here to the datatypes ArrayList and Hashtable.
/// All numbers are parsed to doubles.
/// </summary>
public class JSON
{
	public const int TOKEN_NONE = 0;
	public const int TOKEN_CURLY_OPEN = 1;
	public const int TOKEN_CURLY_CLOSE = 2;
	public const int TOKEN_SQUARED_OPEN = 3;
	public const int TOKEN_SQUARED_CLOSE = 4;
	public const int TOKEN_COLON = 5;
	public const int TOKEN_COMMA = 6;
	public const int TOKEN_STRING = 7;
	public const int TOKEN_NUMBER = 8;
	public const int TOKEN_TRUE = 9;
	public const int TOKEN_FALSE = 10;
	public const int TOKEN_NULL = 11;

	private const int BUILDER_CAPACITY = 2000;

	/// <summary>
	/// Parses the string json into a value
	/// </summary>
	/// <param name="json">A JSON string.</param>
	/// <returns>An ArrayList, a Hashtable, a double, a string, null, true, or false</returns>
	public static object JsonDecode(string json)
	{
		bool success = true;

		return JsonDecode(json, ref success);
	}

	/// <summary>
	/// Parses the string json into a value; and fills 'success' with the successfullness of the parse.
	/// </summary>
	/// <param name="json">A JSON string.</param>
	/// <param name="success">Successful parse?</param>
	/// <returns>An ArrayList, a Hashtable, a double, a string, null, true, or false</returns>
	public static object JsonDecode(string json, ref bool success)
	{
		success = true;
		if (json != null)
		{
			char[] charArray = json.ToCharArray();
			int index = 0;
			object value = ParseValue(charArray, ref index, ref success);
			return value;
		}
		else
		{
			return null;
		}
	}

	/// <summary>
	/// Converts a Hashtable / ArrayList object into a JSON string
	/// </summary>
	/// <param name="json">A Hashtable / ArrayList</param>
	/// <returns>A JSON encoded string, or null if object 'json' is not serializable</returns>
	public static string JsonEncode(object json)
	{
		StringBuilder builder = new StringBuilder(BUILDER_CAPACITY);
		bool success = SerializeValue(json, builder);
		return (success ? builder.ToString() : null);
	}

	protected static Hashtable ParseObject(char[] json, ref int index, ref bool success)
	{
		Hashtable table = new Hashtable();
		int token;

		// {
		NextToken(json, ref index);

		bool done = false;
		while (!done)
		{
			token = LookAhead(json, index);
			if (token == JSON.TOKEN_NONE)
			{
				success = false;
				return null;
			}
			else if (token == JSON.TOKEN_COMMA)
			{
				NextToken(json, ref index);
			}
			else if (token == JSON.TOKEN_CURLY_CLOSE)
			{
				NextToken(json, ref index);
				return table;
			}
			else
			{

				// name
				string name = ParseString(json, ref index, ref success);
				if (!success)
				{
					success = false;
					return null;
				}

				// :
				token = NextToken(json, ref index);
				if (token != JSON.TOKEN_COLON)
				{
					success = false;
					return null;
				}

				// value
				object value = ParseValue(json, ref index, ref success);
				if (!success)
				{
					success = false;
					return null;
				}

				table[name] = value;
			}
		}

		return table;
	}

	protected static ArrayList ParseArray(char[] json, ref int index, ref bool success)
	{
		ArrayList array = new ArrayList();

		// [
		NextToken(json, ref index);

		bool done = false;
		while (!done)
		{
			int token = LookAhead(json, index);
			if (token == JSON.TOKEN_NONE)
			{
				success = false;
				return null;
			}
			else if (token == JSON.TOKEN_COMMA)
			{
				NextToken(json, ref index);
			}
			else if (token == JSON.TOKEN_SQUARED_CLOSE)
			{
				NextToken(json, ref index);
				break;
			}
			else
			{
				object value = ParseValue(json, ref index, ref success);
				if (!success)
				{
					return null;
				}

				array.Add(value);
			}
		}

		return array;
	}

	protected static object ParseValue(char[] json, ref int index, ref bool success)
	{
		switch (LookAhead(json, index))
		{
			case JSON.TOKEN_STRING:
				return ParseString(json, ref index, ref success);
			case JSON.TOKEN_NUMBER:
				return ParseNumber(json, ref index);
			case JSON.TOKEN_CURLY_OPEN:
				return ParseObject(json, ref index, ref success);
			case JSON.TOKEN_SQUARED_OPEN:
				return ParseArray(json, ref index, ref success);
			case JSON.TOKEN_TRUE:
				NextToken(json, ref index);
				return Boolean.Parse("TRUE");
			case JSON.TOKEN_FALSE:
				NextToken(json, ref index);
				return Boolean.Parse("FALSE");
			case JSON.TOKEN_NULL:
				NextToken(json, ref index);
				return null;
			case JSON.TOKEN_NONE:
				break;
		}

		success = false;
		return null;
	}

	protected static string ParseString(char[] json, ref int index, ref bool success)
	{
		StringBuilder s = new StringBuilder(BUILDER_CAPACITY);
		char c;

		EatWhitespace(json, ref index);

		// "
		c = json[index++];

		bool complete = false;
		while (!complete)
		{

			if (index == json.Length)
			{
				break;
			}

			c = json[index++];
			if (c == '"')
			{
				complete = true;
				break;
			}
			else if (c == '\\')
			{

				if (index == json.Length)
				{
					break;
				}
				c = json[index++];
				if (c == '"')
				{
					s.Append('"');
				}
				else if (c == '\\')
				{
					s.Append('\\');
				}
				else if (c == '/')
				{
					s.Append('/');
				}
				else if (c == 'b')
				{
					s.Append('\b');
				}
				else if (c == 'f')
				{
					s.Append('\f');
				}
				else if (c == 'n')
				{
					s.Append('\n');
				}
				else if (c == 'r')
				{
					s.Append('\r');
				}
				else if (c == 't')
				{
					s.Append('\t');
				}
				else if (c == 'u')
				{
					int remainingLength = json.Length - index;
					if (remainingLength >= 4)
					{
						// fetch the next 4 chars
						char[] unicodeCharArray = new char[4];
						Array.Copy(json, index, unicodeCharArray, 0, 4);
						// parse the 32 bit hex into an integer codepoint
						uint codePoint = UInt32.Parse(new string(unicodeCharArray), NumberStyles.HexNumber);
						// convert the integer codepoint to a unicode char and add to string
						try
						{
							s.Append(Char.ConvertFromUtf32((int)codePoint));
						}
						catch (Exception e)
						{
							s.Append("");
						}
						// skip 4 chars
						index += 4;
					}
					else
					{
						break;
					}
				}

			}
			else
			{
				s.Append(c);
			}

		}

		if (!complete)
		{
			success = false;
			return null;
		}

		return s.ToString();
	}

	protected static double ParseNumber(char[] json, ref int index)
	{
		EatWhitespace(json, ref index);

		int lastIndex = GetLastIndexOfNumber(json, index);
		int charLength = (lastIndex - index) + 1;
		char[] numberCharArray = new char[charLength];

		Array.Copy(json, index, numberCharArray, 0, charLength);
		index = lastIndex + 1;
		return Double.Parse(new string(numberCharArray), CultureInfo.InvariantCulture);
	}

	protected static int GetLastIndexOfNumber(char[] json, int index)
	{
		int lastIndex;

		for (lastIndex = index; lastIndex < json.Length; lastIndex++)
		{
			if ("0123456789+-.eE".IndexOf(json[lastIndex]) == -1)
			{
				break;
			}
		}
		return lastIndex - 1;
	}

	protected static void EatWhitespace(char[] json, ref int index)
	{
		for (; index < json.Length; index++)
		{
			if (" \t\n\r".IndexOf(json[index]) == -1)
			{
				break;
			}
		}
	}

	protected static int LookAhead(char[] json, int index)
	{
		int saveIndex = index;
		return NextToken(json, ref saveIndex);
	}

	protected static int NextToken(char[] json, ref int index)
	{
		EatWhitespace(json, ref index);

		if (index == json.Length)
		{
			return JSON.TOKEN_NONE;
		}

		char c = json[index];
		index++;
		switch (c)
		{
			case '{':
				return JSON.TOKEN_CURLY_OPEN;
			case '}':
				return JSON.TOKEN_CURLY_CLOSE;
			case '[':
				return JSON.TOKEN_SQUARED_OPEN;
			case ']':
				return JSON.TOKEN_SQUARED_CLOSE;
			case ',':
				return JSON.TOKEN_COMMA;
			case '"':
				return JSON.TOKEN_STRING;
			case '0':
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
			case '8':
			case '9':
			case '-':
				return JSON.TOKEN_NUMBER;
			case ':':
				return JSON.TOKEN_COLON;
		}
		index--;

		int remainingLength = json.Length - index;

		// false
		if (remainingLength >= 5)
		{
			if (json[index] == 'f' &&
				json[index + 1] == 'a' &&
				json[index + 2] == 'l' &&
				json[index + 3] == 's' &&
				json[index + 4] == 'e')
			{
				index += 5;
				return JSON.TOKEN_FALSE;
			}
		}

		// true
		if (remainingLength >= 4)
		{
			if (json[index] == 't' &&
				json[index + 1] == 'r' &&
				json[index + 2] == 'u' &&
				json[index + 3] == 'e')
			{
				index += 4;
				return JSON.TOKEN_TRUE;
			}
		}

		// null
		if (remainingLength >= 4)
		{
			if (json[index] == 'n' &&
				json[index + 1] == 'u' &&
				json[index + 2] == 'l' &&
				json[index + 3] == 'l')
			{
				index += 4;
				return JSON.TOKEN_NULL;
			}
		}

		return JSON.TOKEN_NONE;
	}

	protected static bool SerializeValue(object value, StringBuilder builder)
	{
		bool success = true;

		if (value is string)
		{
			success = SerializeString((string)value, builder);
		}
		else if (value is Hashtable)
		{
			success = SerializeObject((Hashtable)value, builder);
		}
		else if (value is ArrayList)
		{
			success = SerializeArray((ArrayList)value, builder);
		}
		else if (IsNumeric(value))
		{
			success = SerializeNumber(Convert.ToDouble(value), builder);
		}
		else if ((value is Boolean) && ((Boolean)value == true))
		{
			builder.Append("true");
		}
		else if ((value is Boolean) && ((Boolean)value == false))
		{
			builder.Append("false");
		}
		else if (value == null)
		{
			builder.Append("null");
		}
		else if(value is Dictionary<string, object>)
		{
			success = SerializeDictionary((Dictionary<string, object>)value, builder);
		}
		else
		{
			success = false;
		}
		return success;
	}

	protected static bool SerializeObject(Hashtable anObject, StringBuilder builder)
	{
		builder.Append("{");

		IDictionaryEnumerator e = anObject.GetEnumerator();
		bool first = true;
		while (e.MoveNext())
		{
			string key = e.Key.ToString();
			object value = e.Value;

			if (!first)
			{
				builder.Append(", ");
			}

			SerializeString(key, builder);
			builder.Append(":");
			if (!SerializeValue(value, builder))
			{
				return false;
			}

			first = false;
		}

		builder.Append("}");
		return true;
	}

	protected static bool SerializeDictionary(Dictionary<string, object> anObject, StringBuilder builder)
	{
		builder.Append("{");

		IDictionaryEnumerator e = anObject.GetEnumerator();
		bool first = true;
		while (e.MoveNext())
		{
			string key = e.Key.ToString();
			object value = e.Value;

			if (!first)
			{
				builder.Append(", ");
			}

			SerializeString(key, builder);
			builder.Append(":");
			if (!SerializeValue(value, builder))
			{
				return false;
			}

			first = false;
		}

		builder.Append("}");
		return true;
	}

	protected static bool SerializeArray(ArrayList anArray, StringBuilder builder)
	{
		builder.Append("[");

		bool first = true;
		for (int i = 0; i < anArray.Count; i++)
		{
			object value = anArray[i];

			if (!first)
			{
				builder.Append(", ");
			}

			if (!SerializeValue(value, builder))
			{
				return false;
			}

			first = false;
		}

		builder.Append("]");
		return true;
	}

	protected static bool SerializeString(string aString, StringBuilder builder)
	{
		builder.Append("\"");

		char[] charArray = aString.ToCharArray();
		for (int i = 0; i < charArray.Length; i++)
		{
			char c = charArray[i];
			if (c == '"')
			{
				builder.Append("\\\"");
			}
			else if (c == '\\')
			{
				builder.Append("\\\\");
			}
			else if (c == '\b')
			{
				builder.Append("\\b");
			}
			else if (c == '\f')
			{
				builder.Append("\\f");
			}
			else if (c == '\n')
			{
				builder.Append("\\n");
			}
			else if (c == '\r')
			{
				builder.Append("\\r");
			}
			else if (c == '\t')
			{
				builder.Append("\\t");
			}
			else
			{
				int codepoint = Convert.ToInt32(c);
				if ((codepoint >= 32) && (codepoint <= 126))
				{
					builder.Append(c);
				}
				else
				{
					builder.Append("\\u" + Convert.ToString(codepoint, 16).PadLeft(4, '0'));
				}
			}
		}

		builder.Append("\"");
		return true;
	}

	protected static bool SerializeNumber(double number, StringBuilder builder)
	{
		builder.Append(Convert.ToString(number, CultureInfo.InvariantCulture));
		return true;
	}

	/// <summary>
	/// Determines if a given object is numeric in any way
	/// (can be integer, double, null, etc). 
	/// 
	/// Thanks to mtighe for pointing out Double.TryParse to me.
	/// </summary>
	protected static bool IsNumeric(object o)
	{
		double result;

		return (o == null) ? false : Double.TryParse(o.ToString(), out result);
	}
}

